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Jennifer E. Kay, Marika M. Holland, Cecilia M. Bitz, Edward Blanchard-Wrigglesworth, Andrew Gettelman, Andrew Conley, and David Bailey

atmosphere (TOA) radiative fluxes. For each control integration, we then ran a sensitivity experiment by instantaneously doubling the CO 2 concentration from the 1850 value of 284.7 to 569.4 ppmv. Because the TOA radiative forcing resulting from a CO 2 doubling ( Q 2xCO2 , W m −2 ) depends both on the radiative transfer code and on the climate state, we estimated the Q 2xCO2 separately for CAM4 and CAM5 using one year of offline radiative transfer calculations. We allowed temperatures above the

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Marika M. Holland, David A. Bailey, Bruce P. Briegleb, Bonnie Light, and Elizabeth Hunke

BL07 ); a melt pond parameterization that relates the evolution of pond area and depth to the surface meltwater flux; and the deposition, cycling, and radiative impacts of aerosols on sea ice. These improvements allow for an internally consistent and physically based treatment of sea ice shortwave radiation physics in a coupled climate model, which represents an important step forward in the realism of these processes. Using constrained model experiments, we consider whether this increased

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C. M. Bitz, K. M. Shell, P. R. Gent, D. A. Bailey, G. Danabasoglu, K. C. Armour, M. M. Holland, and J. T. Kiehl

tropopause radiative flux change from doubling CO 2 with stratospheric temperatures adjusted to their new thermal equilibrium for CCSM4. Using the same estimate for CCSM3 is partly justifiable given that the radiation code is the same. However, there is an unknown influence from differences in the mean climate state, which we effectively ignore. The estimate of global mean radiative forcing is only a factor in calculating net feedback (see section 3a ) and effective climate sensitivity (see section 4

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David M. Lawrence, Keith W. Oleson, Mark G. Flanner, Christopher G. Fletcher, Peter J. Lawrence, Samuel Levis, Sean C. Swenson, and Gordon B. Bonan

model; the biogeophysical impact of transient land cover and land use change; the radiative forcing of aerosol deposition onto snow; terrestrial carbon fluxes and their evolution due to land use, wildfire, and net ecosystem production; the improved representation of permafrost; and the impact of prognostic vegetation state on climate variability. A discussion and summary of the strengths and weaknesses of the surface climate simulation within CCSM4 and ways in which CLM4 can be improved and expanded

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Susan C. Bates, Baylor Fox-Kemper, Steven R. Jayne, William G. Large, Samantha Stevenson, and Stephen G. Yeager

match more poorly known 1850 reconstructions, but has a more defensible top of the atmosphere radiative balance. Comparison of the present-day means of heat and freshwater flux fields from the CCSM4 to CCSM3 ( Large and Danabasoglu 2006 ; Hack et al. 2006 ; Collins et al. 2006 ) shows improvement, although many known biases are still present and are sometimes worse ( Fig. 1 ). The global present-day mean bias for the Q as flux indicates an overall increase of heat flux into the ocean with the

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S. J. Ghan, X. Liu, R. C. Easter, R. Zaveri, P. J. Rasch, J.-H. Yoon, and B. Eaton

years analyzed. The year 2000 simulations of the aerosol have been evaluated by Liu et al. (2011) . The mean climate simulated by CAM5 is described by P. J. Rasch et al. (2011, unpublished manuscript). 3. Radiative forcing To estimate the aerosol radiative forcing we express it as a radiative flux perturbation ( Haywood et al. 2009 ; Lohmann et al. 2010 ) calculated from the difference between simulations with the same ocean surface conditions but emissions for years 2000 and 1850. Contrasting

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Peter J. Lawrence, Johannes J. Feddema, Gordon B. Bonan, Gerald A. Meehl, Brian C. O’Neill, Keith W. Oleson, Samuel Levis, David M. Lawrence, Erik Kluzek, Keith Lindsay, and Peter E. Thornton

historical NEE at 0.18 PgC yr −1 , with a much smaller loss in ecosystem carbon at −24.5 PgC and a smaller release of carbon to the atmosphere at 15.4 PgC. As found in the historical period, the CCSM4 RCP 2.6 cumulative wood harvest flux of 136.2 PgC was substantially lower than the GLM wood harvest carbon of 164.6 PgC. The RCP 4.5 GLM land cover corresponded with the lower midrange radiative pathway and had the only decrease in crops of all the RCPs at −4.2 × 10 6 km 2 . This combined with a similar

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A. Gettelman, J. E. Kay, and K. M. Shell

( Soden et al. 2008 ; Shell et al. 2008 ) factors the feedback parameter for each climate variable X into two parts by approximating the change in ( Q − F ) in response to Δ X as linear around some base state. The quantity is the radiative kernel , the change in TOA fluxes due to a standard change in a physical climate variable (the adjoint radiative response). It is calculated using an offline radiative transfer model and depends on the radiative transfer code, as well as the base state

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Jenny Lindvall, Gunilla Svensson, and Cecile Hannay

temperatures at the high-latitude wintertime, which seem to be especially pronounced at nighttime, are connected with too much radiative cooling. Unfortunately, many of the sites lack data of the radiative flux components, and thus it is hard to attribute the cause of this excess cooling. However, since the simulated temperatures are lower than those observed and the shortwave component is small, it is likely that it is due to too little incoming longwave radiation. This cannot explain the differences

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Kirsten Zickfeld, Michael Eby, Andrew J. Weaver, Kaitlin Alexander, Elisabeth Crespin, Neil R. Edwards, Alexey V. Eliseev, Georg Feulner, Thierry Fichefet, Chris E. Forest, Pierre Friedlingstein, Hugues Goosse, Philip B. Holden, Fortunat Joos, Michio Kawamiya, David Kicklighter, Hendrik Kienert, Katsumi Matsumoto, Igor I. Mokhov, Erwan Monier, Steffen M. Olsen, Jens O. P. Pedersen, Mahe Perrette, Gwenaëlle Philippon-Berthier, Andy Ridgwell, Adam Schlosser, Thomas Schneider Von Deimling, Gary Shaffer, Andrei Sokolov, Renato Spahni, Marco Steinacher, Kaoru Tachiiri, Kathy S. Tokos, Masakazu Yoshimori, Ning Zeng, and Fang Zhao

in 2300, while the radiative forcing from non-CO 2 greenhouse gases was held fixed at year-2300 levels. Other forcings were held fixed at the level specified for the RCP simulations. For the GENIE model, CO 2 emissions were set to zero after 2300. It should be noted that in most models, setting the anthropogenic perturbation to zero did not result in zero emissions exactly. The reason is that the 1840–50 land–atmosphere and ocean–atmosphere CO 2 fluxes in response to forcing are not exactly

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